The rotating assemblies of gas turbine engines (e.g., fans, boosters, compressors, and turbines) are typically used to impart or extract energy from a gas flow passing therethrough. These rotatable assemblies typically comprise a rotatable disk or rotor having a plurality of air foil projections or blades disposed thereabout.
While many designs have been proposed in the art, there continues to be a desire to reduce the weight, increase the durability, and improve the mechanical and aerodynamic performances of these rotatable assemblies.
While achieving the above-described benefits is often desirable, the rotatable assemblies and, in particular, the blades attached thereto should also be designed to accommodate vibratory stresses/deflections and aerodynamic loading effects. Often, accommodation of these design requirements is counter to the desire to reduce weight, increase durability, and improve mechanical/aerodynamic performance of the blades. For example, while more aggressive fan airfoil designs having long blade tip chords and forward blade sweep have long been recognized as desirable, such designs typically have undesirably high stresses at the root of the blade and low blade flex and torsion natural frequencies which can be excited by engine operation.
One solution proposed in the art for increasing blade damping (which reduces blade vibrations) has included the use of "part span" blade shrouds. These blade shrouds comprise short discrete elements which are fixedly attached to the tip or at the mid span of each blade. The blade shrouds can rub and/or interlock during engine operation so as to limit blade deflection, blade untwist, and blade camber changes which can occur as a result of the aerodynamic forces acting upon the blades during engine operation. While these blade shrouds can limit deflections and provide some damping, they also produce aerodynamic losses, increase blade weight and blade stress due to the centrifugal forces imparted upon the blades from the added weight and require more robust rotatable disks which can withstand these increased centrifugal forces.
Another solution is proposed in U.S. Pat. No. 5,037,273 to Kueger et al. which teaches a compressor impeller comprising a ring shaped band mounted at the blade tips. Each blade tip is slidably enclosed by a guide block, and the guide blocks are in turn fastened to the ring-shaped band. Filler pieces are provided between the guide blocks. While this design may have been adequate for its intended purpose, it requires numerous structural elements which slidably engage each other, thereby introducing potential wear problems, air leakage and aerodynamic drag problems, and also can add additional weight and attendant undesirable stresses to the band.
As such, there is a continuing desire in the art to provide rotatable assemblies for gas turbine engines which can limit deflections and reduce air leakage and drag, improve blade damping and which are simple, lightweight, and easy to manufacture. Still further, there is a continuing desire to provide rotatable assemblies which can accommodate blades which are lighter and incorporate more aggressive and efficient aerodynamic designs while reducing blade stresses and increasing the blade flex and/or torsional natural frequencies.